Device for Providing Gases, in Particular for Isotopic Ratio Analysis

ABSTRACT

A device is provided for delivering gases to an analyzer, such as an isotopic ratio mass spectrometer. The device includes first and second reactors, preferably arranged in parallel. At least one of the reactors may be selectively activated, or means may be incorporated to circumvent one of the reactors, such that different types of gas conversions may be achieved.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation under 35 U.S.C. §120 andclaims the priority benefit of co-pending U.S. patent application Ser.No. 12/668,011, filed Apr. 29, 2010, which is the United States NationalStage Application, under 35 U.S.C. 371, of International ApplicationPCT/EP2008/005363 having an international filing date of Jul. 1, 2008.The disclosures of each of the foregoing applications are incorporatedherein by reference.

FIELD OF THE INVENTION

The invention relates to an apparatus having an analyzer and having adevice for providing gases for an analysis, in particular fordetermining isotopic ratios, wherein the analyzer is connecteddownstream of the device and the device for providing the gases has afirst gas path for a gas stream, a second gas path and a first reactorbetween the two gas paths, and wherein the first reactor has an inletside and an outlet side and the inlet side of the first reactor facesthe first gas path.

BACKGROUND OF THE INVENTION

A preferred, but not exclusive, application of the invention is that ofmeasuring the isotopic ratios of gases or of substances that have firstbeen transformed into the gas phase. It is known in this connection forvarious analyzers to be used, such as for example mass spectrometers(MS), accelerator MS, optical spectrometers (for example laser-resonancemeasurement), scintillation counters, etc. Preferred analyzers are massspectrometers, such as for example multi-collector sector-field MS,time-of-flight mass spectrometers (TOF-MS) or quadrupole MS, inparticular specifically for the determination of isotopic ratios. Theinvention is preferably used for measuring methane or respiratory gas,for example, and/or for determining the isotopic ratios of carbon,oxygen, nitrogen, sulfur, phosphorus, water vapor/deuterium or chlorinein suitable or appropriately prepared samples. The following moleculesmay be measured for this: N2, CO, 02, H2, CO2, N20, CH4 and/or N02. Thislist is not exhaustive.

In the analyzer, simplest possible gases—one—to three-atom gases withonly one or two different atoms—are measured. In a specificimplementation, gases with more complex molecules may also be analyzed.More complex molecules are generally transformed into simpler moleculesbefore the analysis, by pyrolysis, oxidation and/or reduction.Corresponding reactors or furnaces, or combinations of furnaces, areprovided for this purpose.

Starting materials for the analyses are often liquids or gas mixtures,the constituents of which are separated from one another over time in agas chromatograph.

Altogether, the apparatus used comprising the gas chromatograph,furnaces for gas conversion and the analyzer is quite complex. Inparticular in the area of gas conversion, the arrangement of theindividual component parts of the apparatus can be varied in many ways.A slightly different construction is required for virtually every typeof conversion. For the user, this is laborious and susceptible to error.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a device for providinggases for an analysis in which different measurements are possiblewithout changing the construction. In particular, it is intended thatdifferent gas conversions can be carried out with the device.

The apparatus according to the invention is characterized by at leastone second reactor, which is arranged parallel to, or in series with,the first reactor, wherein at least one of the reactors can bedeactivated or means are provided for circumventing at least one of thereactors.

The second reactor allows additional or alternative thermal measures tobe applied to the gases supplied, so that different measurements arepossible one after the other in an extremely short time. The reactorsmay be arranged and connected parallel to one another, for example withinterconnected inlet sides or outlet sides. Preferably, the inlet sidesof the reactors are interconnectable and so are the respective outletsides. Furthermore, a common gas path may be provided for the supply ofthe gases to the two reactors. Finally, a common gas path may also beprovided for the passing on of the gases from the two reactors in thedirection of a downstream analyzing device.

An arrangement or connection of the reactors in series is also possible.This means that the inlet side of one reactor can be interconnected withthe outlet side of the other reactor. During operation, both reactors oronly one of the two reactors then operate(s). In addition, the reactorsmay have bypass lines, so that for example the gas can be made to bypassan inactive reactor.

Advantageously, the second reactor is arranged parallel to the firstreactor, downstream of the first gas path, wherein switching devices forswitching over the gas stream are provided in such a way that the gasstream coming from the first gas path, or a main part thereof,optionally passes into the first reactor or into the second reactor.Furthermore, a first switching device for switching over the gas streammay be provided. Preferably, only this single switching device forswitching over the gas stream is provided. The switching has the effectthat the gas stream passes into the first reactor by way of the inletside thereof or into the second reactor by way of the inlet sidethereof.

With the switching device provided, it is possible to switch back andforth between the two reactors for carrying out different gasconversions. The switching may be provided in such a way that the gasstream in the first gas path is made to pass completely via the firstreactor or the second reactor. Alternatively, a division of the gasstream may take place in such a way that a large part of the gas streamis made to pass via one reactor and a small fraction of the gas streamis made to pass via the other reactor. Maintaining at least a small gasstream in the reactor helps to avoid dead volumes, inactive times andresultant measuring errors and hysteresis effects. The limiting case ofdividing the gas stream in half between the reactors is of course alsopossible. A continuous gas flow through the reactors is also desired.

According to a further idea of the invention, the first switching deviceis provided between the second gas path and the outlet sides of the tworeactors. Accordingly, the switching device is arranged downstream ofthe reactors. A simple branching arrangement may be provided upstream ofthe reactors, between the first gas path and the two reactors, so thatgas can always pass into the two reactors. An advantage of this solutionis that any high gas temperatures that may occur upstream of thereactors do not heat up the switching device. Furthermore, a steady flowthrough both reactors can be obtained. During switching, there are thenno inactive times and there is no need to allow for dead volume.Finally, contamination of the switching device by analytes that arestill organic upstream of the reactors is avoided.

Preferably, the first switching device is arranged in such a way that itoptionally connects the second gas path to the first reactor or to thesecond reactor, to be precise to an outlet side of the respectivereactor.

Alternatively, the switching device may of course also be arrangedupstream of both reactors, and would then be arranged between the firstgas path and the inlet sides of the reactors. This would then easilyallow the effect to be achieved that only one of the two reactors issteadily flowed through by the gas.

According to a further idea of the invention, a third gas path and asecond switching device are provided, wherein the second switchingdevice optionally connects the third gas path to the first reactor or tothe second reactor. Preferably, the switching takes place in such a waythat the third gas path is connected to the first reactor or secondreactor instead of the second gas path, to be precise on the outlet sideof the reactors.

According to a further idea of the invention, the first switching deviceis combined with the second switching device to form a single switchingdevice. Preferably, a multi-way valve (4/2-way valve) is provided,arranged between the two reactors on the one hand and the two gas pathson the other hand (second and third gas paths), and assignment of eachof the two reactors to one of the two gas paths is made possible.

According to a further idea of the invention, the third gas path has adifferent, in particular higher flow resistance than the second gaspath. The ratio of the mass flows or volume flows in the gas paths canbe set by way of the flow resistance. The flow resistance may be formedas a constant or variable restriction. As a result, the volume flowalong the gas paths can be controlled and can be changed continuously orabruptly. This avoids fractionating effects during the switching of thegas paths.

Preferably, the flow resistance in the third gas path is realized by adefined constriction or a valve or a constriction with an adjustablecross section. Preferred is an embodiment in which only a very smallproportion is made to pass by way of the third gas path, for exampleonly 5% of the volume flow, white 95% flows through the second gas path.

According to a further idea of the invention, it is provided that thetwo reactors are arranged in series one behind the other in such a waythat an outlet side of one reactor is connected or can be connected toan inlet side of the other reactor, and that preferably at least one ofthe two reactors is provided with a bypass line which can optionally beconnected to the other reactor, respectively. It is also possible forboth reactors to have a bypass line. As a result, it is possible to makethe gas optionally pass by one of the reactors and be thermally treatedin the other reactor, respectively. A solution without a bypass line isalso possible, however. The gas would then pass through both reactorsone after the other and be thermally treated either only in one of thereactors or in both one after the other. Preferably, higher temperaturesare provided in the second reactor in the direction of flow than in thefirst reactor. The arrangement may also be reversed, however. The sametemperatures may also be provided.

According to a further idea of the invention, the reactors are arrangedparallel to one another, wherein an additional gas source and switchingdevices are provided in such a way that optionally one of the tworeactors is connected between the first gas path and the second gas pathand the other reactor is connected to the additional gas source. Thisconstruction is advantageous in particular for the regeneration of thereactors. For example, a regenerating gas may flow from the additionalgas source into the reactor, while the other reactor, respectively, isused for the preparation of gases for analysis. Instead of regeneration,a simple flushing operation may also be provided. The additional gassource may alternatively be arranged upstream or downstream of thereactors.

According to a further idea of the invention, it is provided that thefirst gas path leads to the first reactor, that a further gas path leadsto the second reactor and that a dedicated gas source, in particular adedicated gas chromatograph or a dedicated gas chromatography column, isarranged upstream of each of the gas paths. As a result, each reactorreceives gas from a dedicated source. The sources or gas chromatographsmay provide gases independently of one another.

According to a further idea of the invention, the first switching deviceor a further switching device may be provided between the inlet sides ofthe two reactors and the first gas path. The two reactors may also beeach assigned a switching device on their inlet sides and their outletsides. As a result, it is possible to carry out the switching optionallyin the region of the inlet sides or the outlet sides.

According to a further idea of the invention, the first gas path isprovided with a connecting location for a branch. The branch can then beused for a return flow of the gas or backflushing of the reactors. Inthis way, the gas arriving in the first gas path can be dischargedbefore it enters the reactors. If a switching device is arranged in theregion of the inlet sides of the reactors, the connecting location forthe branch also lies upstream of the switching device.

According to a further idea of the invention, the second gas path isprovided with a connecting location for a branch, in particular forconnection to a gas supply. The same may also be provided for the thirdgas path. Gases for the backflushing of the reactors or for otherpurposes may be introduced by way of the branches. Oxygen forregenerating an oxidation reactor or helium as an additional carrier gasmay be supplied in this way.

According to a further idea of the invention, the reactors can be heatedup to different temperatures, in particular for pyrolysis on the onehand and oxidation on the other hand. Depending on the application,different reactions may be desired.

According to an independent aspect of the invention, the reactors arearranged in a common housing with at least partly common insulation. Onaccount of the high temperatures, the reactors are surrounded by aheat-insulating wall. To minimize the heat that is lost, the reactorsare arranged adjacent one another, so that they thermally influence oneanother or the lost heat of the hotter reactor contributes to theheating up of the cooler reactor. The reactors are at least partlysurrounded by a common insulating wall.

According to a further idea of the invention, the housing has at leastone insulating layer with an outer side and an inner side, one of thereactors being arranged closer to the outer side than the other reactor.Ambient temperature prevails on the outer side of the housing. There isa temperature gradient from the outer side to the hottest reactor. Theless hot reactor is arranged along the temperature gradient.

Preferably, at least one of the two reactors is arranged in theinsulating layer. As a result, a distinct change in temperature can alsobe achieved between the two reactors. The hotter reactor is thenpreferably provided in a chamber surrounded by the insulating layer.

Both reactors may be assigned thermocouples for controllingcorresponding heaters. Both reactors may also each be assigned at leastone heater. The reactors may then be heated up independently of oneanother. Alternatively, it is also possible for only one heater to beprovided, in particular within the chamber surrounded by the insulatinglayer, either for both reactors together or for one reactor, so that theother reactor is heated by the lost heat.

According to a further idea of the invention, both reactors are eachassigned at least one heater, the heater provided for the reactor thatis arranged closer to the outer side being less powerful than the heaterof the other reactor. The inner reactor (greater distance from the outerside) is then provided with the main heater, while the outer heater hasonly a supplementary heater. The desired temperatures are preferably aminimum of 800° C. (outer reactor) and a maximum of 1600° C. (innerreactor).

According to a further idea of the invention, the device has aninterface for the connection of an optical detector or a massspectrometer, in particular an isotope mass spectrometer. Such aninterface may be, for example, an open split. Other interfaces are alsopossible. Preferably, the interface is arranged downstream of the secondgas path or is connected to it.

According to a further idea of the invention, a third reactor isprovided, arranged along the second gas path, in particular a reductionreactor. This may be operated in particular in connection with anoxidation reactor as the first or second reactor.

Advantageously, the first gas path has a connecting location with abranch or a line to a detector. The connecting location may beswitchable by a valve—also in the line itself—or a restriction on theline. With the aid of the detector before the gases enter the reactors,additional measurements can be carried out.

According to a further idea of the invention, the gas paths are at leastpartly formed by inertized metal lines. The lines are usuallycapillaries. These are, for example, produced from metal and inertizedon the inner wall. Such lines are robust with respect to thermal andmechanical stress. In particular, lines of steel or high-grade steelwith special coatings are used. Corresponding material combinations areknown under the trade names Silcosteel, SileInert, MXT and others.

A typical reactor is a thin tube that is heated from the outside and inwhich the gas molecules are oxidized, reduced or react in some other wayafter being supplied with heat. The reactor tube is arranged in afurnace with an insulating wall or is pushed into the furnace. Arrangedupstream of the reactor there may be a gas chromatograph or otherseparating device, which breaks down the individual constituents of asample over time and so gradually supplies them to the reactor tube. Thearrangement of a gas chromatograph/separating device following on afterthe reactors, for separating the reaction products over time, is alsopossible.

For carrying the gases to the reactor tube and following on after thereactor tube, relatively thin lines are provided. For the sake ofsimplicity, these lines and the usually comparatively thicker reactortube are referred to hereafter as capillaries and must be connected toone another in a gastight and reliable manner to achieve reproducibleresults. Screw connections between the capillaries, in particular wherethe gases enter the reactor tube and where they leave the same, havebeen customary so far. The screw connections can be easily released andmake it possible for individual capillaries to continue to be when theother capillaries, respectively, that were previously connected areexchanged. One disadvantage of the screw connections or other releasableconnections in this area is the great risk of leakage, for instancecaused by temperature fluctuations and the breaking off of the thintubes during assembly.

Advantageously, the capillaries are connected to one another by bonding,adhesion or pressing. A soldered connection to metal or previouslymetallized surfaces is also within the scope of the invention. The typesof connection mentioned are intended to lead to a gastight andpreferably non-releasable connection of the capillaries. When thecapillary-like reactor tube is exchanged, the capillaries respectivelyconnected to it, which are generally thinner, are also exchanged at thesame time. The costs thereby incurred for the thinner capillaries arenegligible, or even overcompensated by the then obviated screwconnections. The new solution is not only more reliable than the knownsolution but may also be less costly.

According to a further idea of the invention, the capillaries havedifferent diameters and overlap one another, at least with end regions,the end regions being connected to one another (in the region of theoverlap or part of the same). The different diameters make it possibleto push the capillaries to be connected into one another and so achievean overlap.

Advantageously, the capillaries are connected to one anothertwo-dimensionally. The strength and gastightness of the connection arethereby increased. “Two-dimensionally” means that bonding, adhesion orpressing occurs in more than just a punctiform or linear manner. Inparticular, “two-dimensionally” relates to an extent in the axialdirection and at the same time in the circumferential direction.

At least one of the capillaries may consist of ceramic material. Inparticular, the capillary-like reactor tube, or at least the innersurface thereof, consists of a ceramic material, for example in the caseof an H2 reactor. At least a great heat resistance is an advantage.

Advantageously, at least one of the capillaries consists at least partlyof quartz glass, in particular an outer and/or inner surface, forexample in the case of an H2 reactor. Synthetic quartz glass or silicaglass, also known as fused silica, are particularly well suited. Socalled Silcosteel capillaries are also well suited.

According to a further idea of the invention, it is provided that theoverlapping region has at least one bonding connection or adhesiveconnection in the region of a coating of one of the capillaries. Bondingagents or adhesive agents are distributed all around the capillary, i.e.in the circumferential direction. In particular, these are gastightbonding agents or adhesive agents. An example of a gastight adhesive isa polyimide-based adhesive. Different adhesives may also be provided indifferent temperature zones, for example one adhesive for the stabilityof the connection and one adhesive for the sealing.

According to a further idea of the invention, it is provided that theoverlapping region has at least one bonding connection or adhesiveconnection in the region outside the coating. Here, too, the bondingagent or adhesive agent is preferably provided all around, the agentsused being particularly heat-resistant. “Heat resistant” in this sensemeans that the connection is preserved even at temperatures of 300° C.to 400° C. or more, for example at more than 600° C. to 800° C. or evenover 1000° C.

Advantageously, at least one of the capillaries consists at least partlyof nobel metal. This is in particular copper, ruthenium, rhodium,palladium, silver, rhenium, osmium, iridium, platinum or gold. Adequatestrength is important for the corresponding application area. Non-nobelmetals may also be used with preference, for example nickel, inparticular for reactor tubes. Metallic or metallized capillaries maypreferably also be soldered.

Advantageously, one of the capillaries is provided in the overlappingregion with a platinum surface and the other capillary is provided witha ceramic surface preferably in the case of a C02 reactor. Of course,the two capillaries may also respectively consist completely of platinumor ceramic material. Platinum is relatively soft in comparison with theceramic material and, when under pressure—by pressing—fills the roughsurface of the ceramic material, so that a particularly intimate andgastight connection is produced.

Advantageously, at least one of the capillaries is provided with aninertized surface, in particular on the inside. A reaction with the gasflowing through and/or bonding agent or adhesive agent is then unlikely.A capillary is inertized for example with a Silcosteel coating. Otherless reactive surfaces, such as for example platinum, are alsofavorable.

According to a further idea of the invention, a furnace for the thermaltreatment of gases is provided, wherein a reactor tube similar to acapillary and a heater are arranged in a furnace and an insulation isprovided, with the reactor tube and/or a capillary being led through theinsulation, and wherein the reactor tube and the capillary are connectedto one another. The reactor tube has in this case the function of acapillary and is connected in the sense described above to the (other)capillary. Preferably, the reactor tube is respectively connected atboth its ends to a thinner capillary.

According to a further idea of the invention, the capillary connected tothe reactor tube has an outer coating, in particular of anon-heat-resistant material, preferably such as polyimide, the coatingbeing removed where the capillary reaches into the insulation from theoutside. The high temperature prevailing inside the furnace decreasesperpendicularly to the insulation up to the outer side. In order as faras possible not to expose the coating to thermal stress, removal of thesame to the outside of the insulation of the furnace is advantageous. Inthis case, there may also be overlapping between the thinner capillaryand the reactor tube in the region of the removed coating. The coatingis preferably from polyimide. Assumed here as heat-resistant is amaterial that withstands temperatures of at least 300° C., preferablyalso over 400° C., without reacting and/or significantly losingstrength.

Advantageously, the apparatus according to the invention is providedwith an analyzer, in particular a mass spectrometer, connecteddownstream of the device. In this case, a gas chromatograph may beconnected upstream of the device. This gas chromatograph is thenconnected upstream of the first gas path.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention otherwise emerge from the descriptionand from the claims. Advantageously exemplary embodiments of theinvention are explained in more detail below on the basis of drawings,in which:

FIG. 1 shows a schematic representation of an apparatus according to theinvention,

FIG. 2 shows part of an apparatus according to FIG. 1 with a switchingdevice switched in a certain way,

FIG. 3 shows the detail according to FIG. 2, but in a differentswitching position of the switching device,

FIG. 4 shows a furnace with two reactors in a perspectiverepresentation,

FIG. 5 shows the furnace according to FIG. 6 in a vertical section,

FIG. 6 shows the furnace according to FIG. 5 in a horizontal section,

FIG. 7 shows alternatives a) and b) for a bonding connection ofcapillaries in the region of a heat-insulating furnace wall,

FIG. 8 shows a further embodiment of the apparatus according to theinvention in a schematic representation analogous to FIG. 1,

FIG. 9 shows a further embodiment of an apparatus according to theinvention in a representation analogous to FIGS. 2 and 3, and

FIG. 10 shows a further embodiment of the invention in a representationanalogous to FIG. 1.

DETAILED DESCRIPTION OF EMBODIMENTS OF INVENTION

For the analysis of gases in a detector 10, in particular a massspectrometer for determining isotopic ratios, a gas sample coming from agas chromatograph 11 is passed through a furnace 12 and fed to thedetector 10 by way of an interface 13, for instance an open split.

From a GC column 15 connected to an injector 14, a first gas path 16leads by way of a branching arrangement 17 (T piece) and branches (gaspaths) 17 a, 17 b to inlet sides of two reactors 18, 19 arrangedparallel to one another in the furnace 12. Lines (gas paths) 20, 21 leadfrom the outlet sides of the reactors 18, 19 out of the furnace 12 to acommon switching device 22, which is formed here as a 4/2-way valve.

The valve (the switching device 22) allows the reactors 18, 19 to beoptionally connected to a second gas path 23 or alternatively to a thirdgas path 24. The second gas path 23 leads to the interface 13, while thethird gas path 24 is provided with a defined restriction 25, so that thethird gas path 24 has a much greater flow resistance than the second gaspath 23.

The terms “inlet sides” and “outlet sides” refer to a main direction offlow, that is from the gas chromatograph 11 to the detector 10. Theindividual gas paths, lines and branches are formed in particular ascapillaries. The reactors 18, 19 are also preferably capillary-liketubes or reactor tubes.

The two switching positions of the switching device 22 are reproduced inFIGS. 2 and 3. According to FIG. 2, in a switching position I of theswitching device 22, the gas is fed from the first gas path 16 to thehigh-temperature reactor 18 (oxidation reactor) and passes from there byway of the switching device 22 into the second gas path 23. By contrast,in this switching position I, the reactor 19 that is not heated asstrongly (pyrolysis reactor) is connected to the third gas path 24. Intheory, the gas coming from the first gas path 16 can flow via bothreactors 18, 19 and pass either into the second gas path 23 or the thirdgas path 24. In fact, due to the restriction 25 (as a cross-sectionalconstriction), there is a clear disequilibrium in the distribution ofthe volume flows in favor of the second gas path 23. Only 5% to 10% ofthe gas passes into the third gas path 24. Consequently, in thisswitching position I, the gas flowing via the reactor 18 ultimatelypasses into the detector 10. A configuration of the device or therestriction with a smaller disequilibrium of the volume flows up to a50:50 distribution is also possible. With increasing secondary flow, thesignal amplitude at the detector becomes smaller.

In the other switching position II of the switching device 22, the tworeactors 18 1 19 are likewise connected to the second gas path 23 andthe third gas path 24, but in exactly the opposite way to thatpreviously described. Consequently, in the switching position II, thegas flowing via the reactor 19 passes by way of the second gas path 23to the detector 10. Here, too, approximately 5% of the total amount ofgas flows via the other reactor (here the reactor 18) into the third gaspath 24.

Depending on the application and construction of the reactors, the gasstreams may also be divided between different reactors 18, 19 in such away that one of the reactors is regenerated by the gas stream while thesample is thermally treated in the other reactor. The regeneration mayalso refer, for example, to the buildup of layers of carbon.

To extend the functions, the apparatus optionally as additionalcomponent parts:

In the first gas path 16, a branching arrangement 26 with a branch 27 toa detector 28 may follow on after the GC column 15. This detector iseither an additional detector or the branch 27 is merely a bypass andleads to the detector 10 while circumventing the furnace 12. The numbers28 and 10 would then refer to the same component.

A further branching arrangement 29 is fitted into the first gas path 16,in particular between the branching arrangements 17 and 26. Thebranching arrangement 29 leads by way of a branch 30 and a valve 31 outof the GC 11. Optionally, a volume-flow measuring device 32 is providedto follow on after the valve 31.

A water trap 33, in which the moisture present in the gas stream isseparated and carried away, is provided in the second gas path 23.Preferably, a separation of the moisture may take place at awater-permeable membrane with a carrier gas counterflow. Helium ispreferably used as the carrier gas.

A further reactor 34, in particular a reduction reactor, may be providedin the second gas path 23, in particular arranged upstream of the watertrap 33. This further reactor may operate together with one of thereactors 18, 19, so that for example an oxidation and reduction of theflowing gases can be carried out one after the other. In addition oralternatively, a further reactor 35 may be arranged along the line 20.This is also preferably a reduction reactor.

The second gas path 23 may have a branching arrangement 36 with a branch37 and a connection or valve 38 for a gas source. For example, helium orsome other inert gas that can be used for backflushing or regeneratingthe reactors may be fed in by way of the branch 37. Preferably, some orall of the branching arrangements are switchable, so that the gas pathscan be exactly set. Backflushing is then possible, for example, in theswitching position according to FIG. 1 via the lower reactor 19 and thebranch 30. It is also possible for a counter pressure to be produced inthe second gas path 23 by opening the valve 38, so that the gas corningfrom the GC column 15 does not pass into the reactors 18, 19 but isseparated by way of the branch 30. For example, it may be advisable notto direct solvent peaks into the reactors and/or detectors. The valves,for example valve 38, for opening and closing a line or a branch mayalso have a further switching position, that is a leakage position toavoid pressure increases.

The third gas path 24 may have a branching arrangement 39, which may beconnected to a gas source by way of a branch 40 and a valve 41.Preferably, the provision of gas for the regeneration of the oxidationreactor 18 is envisaged here. Suitable gases are oxygen, methane, etc.If and when required, the other reactor 19 may also be optionallyregenerated with a substance connected to the valve 41.

For the measurements, the gases or substances may be brought togetherwith carrier gas, for example with helium or hydrogen, in particularbefore they enter the GC 11 or at some other desired location.

The construction of the furnace 12 with the reactors 18, 19 is explainedin more detail below on the basis of FIGS. 4 to 6:

The furnace 12 may be of a substantially cuboidal form. Other externalconfigurations are possible. A housing 42 is provided on the inside witha thick insulation 43. Depending on the stability of the insulatinglayer 43, the housing 42 may also be omitted. The number 42 then refersto the outer side of the insulating layer 43.

Formed in the furnace 12 is a chamber or a furnace space 44, which isempty or filled with insulating material, for example mineral wool,perlite or other temperature-resistant substances. Arranged in thefurnace space 44 are heating elements 45, 46, the supply lines 47, 48 ofwhich—which may at the same time be mountings—are led through theinsulating layer 43.

The reactors 18, 19 are thin, capillary-like tubes, in particular ofceramic, and preferably run transversely through the furnace 12 parallelto one another at a distance and horizontally directed. In this case,the reactors 18, 19 may be respectively surrounded by a protective tube49, 50, in particular of metal or some other material that conducts heatas much as possible.

The reactors 18, 19 and protective tubes 49, 50 extend through theinsulating layer 43 and protrude slightly beyond the housing 42, or theouter side of the insulating layer 43, the reactors 18, 19 somewhatfurther than the protective tubes 49, 50, see FIG. 6.

The reactor 18 is provided here as a high-temperature reactor and isheated by the heating elements 45, 46 on sides lying opposite oneanother, and at the same time over a number of portions of its length.Correspondingly, two pairs of heating elements 45, 46 are depicted inFIG. 6. In this case, the heating elements 45, 46 and the reactor 18 arearranged completely within the furnace space 44.

The reactor 19 runs within the insulating layer 43, that is between aninner side 51 of the same and the housing 42 or the outer side. In thepresent case, the reactor 19 is arranged in the region of a transitionbetween an upright wall and a bottom at of the insulating layer 43.

In the present case, the reactor 19 is provided with a supplementaryelectrical heater 52, see FIG. 5. This is arranged in the protectivetube 50. A corresponding electrical supply line 53 is laid in theintermediate space between the reactor 19 and the protective tube 50,see FIG. 6.

During operation, the temperature of the reactor 18 is set by theheating elements 45, 46. Temperature sensors that are not shown may beprovided for this purpose. Some of the heat also passes to the reactor19, which as a result is heated slightly less than the reactor 18. If anexact temperature setting is desired for the reactor 19, this can becarried out by means of the supplementary heater 52. Without the effectof the supplementary heater, the temperature of the reactor 19 isdetermined by the power of the heating elements 45, 46 and the positionof the reactor 19 within the insulating layer 43 together with theoutside temperature. In the most favorable case, it is possible todispense with the operation of the supplementary heater 52.

The supply lines 47, 48 are preferably laid approximately horizontallyin an upper region of the furnace space 44 and angled away there in thedownward direction, so that the heating elements 45, 46 lieapproximately halfway up the furnace space 44, as does the reactor 18.

The insulating layer 43 preferably consists of ceramic fiber blocks,mineral wool, chamotte or other materials with good heat insulation.

The reactors 18, 19 are connected to the capillary-like lines 17 a, 17 band 20, 21 by suitable connecting elements, bonding, adhesion orpressing. This is explained in more detail below on the basis of FIGS. 1and 7 with the alternatives a) and b).

In the gas chromatograph (GC column 15), the substances contained in asample are separated from one another over time. In the subsequentfurnace 12, an oxidation, reduction, gasification or pyrolysis takesplace. The temperatures occurring lie distinctly above the ambienttemperature that otherwise acts on the apparatus.

The gaseous substances are carried in the capillary-like lines 16, 17 a,17 b, 20, 21 (FIG. 1). These consist of synthetic quartz glass, which isalso referred to as fused silica. A composite with other materials ispossible. Preferably, however, here the lines consist exclusively ofsynthetic quartz glass with a coating.

In another embodiment, the lines are produced from metallic material, inparticular from high-grade steel, which has a surface coating for thepurpose of inertization. Coatings for steels or high-grade steels areknown by the name Silcosteel (registered trademark).

Capillaries are likewise provided within the furnace 12, that is thereactor tubes 18, 19, the ends 54 of which emerge from the furnace 12,see FIG. 7 alternative a). The reactor tubes 18, 19 usually consist of aceramic material and, depending on the application, are heated up toapproximately 800° C. to 1600° C. Substances that are consumed or can bereactivated may be provided in the reactor tubes to promote theoxidation, pyrolysis or other reactions. A thermally assisted reductionof gaseous substances is also possible in the furnace 12.

In the case of known solutions, the lines are connected to the ends ofthe reactor tubes by screw connections. The aim of this is to make itpossible for the reactor tube to be exchanged while retaining the lines.The known screw connections may, however, cause problems that disturbthe analysis considerably. For instance, teaks or dead volumes may occur(in particular in the case of difficulties during assembly).

Instead of the known solution, in the case of the present exemplaryembodiment according to the invention the line 20 is connected to theadjacent end 54 of the reactor tube 18 non-releasably, in particular bydirect bonding. Known adhesives, in particular high-temperatureadhesives, are suitable as bonding agents. The bonding agents may beselected on the basis of the desired properties, such as grain size ofthe filler, temperature resistance, elasticity, thermal expansion, etc.

An embodiment with two adhesives of different properties is alsopreferred. A high-temperature adhesive provides for the connection to beof adequate strength. A further adhesive, for example with polyimide,increases the sealing. The sealing adhesive may also be subsequentlyinjected into the first adhesive.

Instead of the bonding connection, a connection by adhesion may also beprovided. In this case, agents for improving the adhesion may be used.Such agents may at the same time also be bonding agents.

The end 54 of the reactor tube emerges from a heat-insulating wall 56 ofthe furnace 12, and consists of a ceramic material. The line 20 is afused silica capillary and is provided on the outside with a coating ofpolyimide. The coated part of the line 20 is provided in example a) ofFIG. 7 with the number 57. The coating has been removed from one end 58of the line 20, since here the coating is not heat-resistant. Here, theline 20 and the end 54 are bonded to one another twice, that is on theone hand with a first bonding location 59 between the non-coated end 58and the end 54. In this case, the bonding location 59 preferably lies inthe interior of the furnace 12 and is formed by a high-temperatureadhesive. A second bonding location 60 is formed between the end 54 andthe coated part 57 outside the wall 56. The bonding agent may be lessheat-resistant here. Preferably, a bonding agent that is adapted to theproperties of the coating, in particular a polyimide adhesive, is used.

The connection of the lines 17 a, 17 b to the reactor tubes 18, 19 maybe formed by analogy with the previous embodiments. However, thermallyinsensitive materials are also to be preferred here for the lines 17 a,17 b and the corresponding bonding agents because of the possible highertemperatures following the gas chromatograph 15.

On account of the described bonding between the lines and the reactortubes, these connecting locations are reliable and durably tight. Thereactor tubes and lines are connected to another non-releasably and, ifand when required, are exchanged together. Releasable connections orbranching arrangements are provided for this purpose between the lines17 a, 17 b, 20, 21 on the one hand and the branching arrangement 17 orthe switching device 22 on the other hand. Such releasable connectionsare known and do not require any further explanation. Alternatively, thelines may also be coupled to the gas chromatograph 15 on the one handand the cooling trap 33 on the other hand, or to further component partsof the apparatus, by way of releasable connections.

If a highly heat-resistant line 20 is used, it may also be led throughthe wall 56 into the furnace 12 and end there, see example b) of FIG. 7.Correspondingly, here the end 54 of the reactor tube does not reach asfar as the wall 56 in the interior of the furnace 12. The providedbonding location 59 is highly heat-resistant.

FIG. 8 shows a series connection of the two reactors 18, 19. The reactor18 is connected to the first gas path 16 by way of the branchingarrangement 17. In the branch 17 a there is an activatable valve 61.From the branching arrangement 17, a bypass line 62, provided with anactivatable valve 63, runs parallel to the reactor 18.

The line 20 connects the reactor 18 to the second reactor 19 and has twobranching arrangements 64, 65. The bypass line 62 opens out into thebranching arrangement 64. From the branching arrangement 65, a furtherbypass line 66 runs parallel to the reactor 19 up to a branchingarrangement 67 in the line 21 following the reactor 19.

Activatable valves are also provided between the reactor 18 and thebranching arrangement 64 (valve 68), between the branching arrangement65 and the reactor 19 (valve 69), in the bypass line 66 (valve 70) andbetween the branching arrangement 67 and the reactor 19 (valve 71).

In FIG. 8, only the interface 13 and the detector 10 are depicted asfollowing on after the line 21. In fact, further component parts of theapparatus may be provided, for example the parts depicted in Figurebetween the switching device 22 and the interface 13.

With the device shown in FIG. 8, it is possible to feed the gas producedor provided optionally to one of the two reactors or even to bothreactors one after the other. If appropriate, the inactive reactor iscooled. By way of the controlled valves, the gas may be made to pass byone or both of the reactors. Depending on the application and type ofreactor, backflushing or outgassing processes may be prevented by thevalves mentioned. In this case, the representation according to FIG. 8is to be understood as being purely schematic. In fact, the two reactorsmay also be spatially arranged next to one another in parallel. Theseries connection of the reactors is then obtained by correspondingrouting of the lines mentioned, in particular the line 20.

FIG. 9 also shows special aspects with regard to the mode of operationand construction. Here, the two reactors 18, 19 are intended foralternating analyzing and regenerating operation. The switching device22 that is also shown in FIG. 1 is arranged downstream of the tworeactors. A switching device 72 with the same or similar functionalityis also arranged upstream of the reactors 18, 19. In addition to thebranches 17 a, 17 b, a gas source, for instance the gas chromatograph11, is connected to the switching device 72 by way of the gas path 16,and a gas receiver 74, in particular for deposited gases that cannot beused any further and, for example, are to be filtered or chemicallyconverted, is connected to said switching device by way of a further gaspath 73.

A gas source 76, which preferably provides gas for the regeneration ofthe reactors 18, 19, for example in counterflow, is connected to theswitching device 22 by way of a line 75. During operation, it is alwayspossible to carry out an analysis with the inclusion of one of thereactors 18, 19, while a regeneration process takes place in the otherreactor, respectively, and the gas thereby flowing in the oppositedirection through the regenerating reactor is fed to the gas receiver74. In FIG. 9, the lower reactor 19 is in the process of regenerating,while gas for the analysis is being thermally treated by the upperreactor 18. The gas to be analyzed passes by way of the switching device22 into the second gas path 23 to the detector 10. Further componentparts of the device of various functionalities may be provided along thegas path 23, for example by analogy with FIG. 1.

The two reactors 18, 19 may each be assigned dedicated furnaces withdedicated insulation 77, 78. Alternatively, the reactors 18, 19 may alsobe arranged in a common furnace with common insulation corresponding tothe furnace 12 in FIG. 1.

the embodiment according to FIG. 10, two gas chromatographs or one gaschromatograph 11 with two GC columns 15, 15 a is/are arranged upstreamof the two reactors 18, 19. The GC column 15 is connected to the reactor19 by way of the gas path 16. In the gas path 16, the branchingarrangement 26 with the branch 27 and the detector 28 is provided in away corresponding to FIG. 1. Parallel thereto, the GC column 15 a isconnected to the reactor 18 by way of the gas path 16 a. An injector 14a is arranged upstream of the GC column 15 a. Furthermore, a branchingarrangement 26 a with a branch 27 a and a connected detector 28 a liesin the gas path 16 a.

The two injectors 14, 14 a with the GC columns 15, 15 a may provide gassamples independently of one another.

In the embodiment according to FIG. 10, a switching device correspondingto the switching device 72 my be provided between the gas paths 16, 16 aand the reactors 18, 19, as in FIG. 9, together with the branches 17 a,17 b shown there. The GC columns 15, 15 a may then be optionallyconnected to one of the two reactors 18, 19.

Instead of the GC 11 or the GC columns 15, 15 a, other sources for thesubstances to be analyzed may also be provided, for example liquidchromatographs, evaporators, etc.

1. A method for analyzing gases by isotopic ratios comprising: providinga stream of gas and a branch, the branch leading to an inlet end of atleast a first and a second reactor; in a first mode of operation,passing gas from an outlet end of the first reactor to a downstreamisotope ratio analyzer; in a second mode of operation, passing gas froman outlet end of the second reactor to the downstream isotope ratio massanalyzer; and determining an isotope ratio with the isotope ratio massanalyzer.
 2. The method according to claim 1 wherein the at least firstand/or the second reactor contains an oxidizing agent that oxidizescomponents in the gas stream.
 3. The method according to claim 1 whereinthe at least first and/or the second reactor contains a reducing agentthat reduces components in the gas stream.
 4. The method according toclaim 1 wherein the at least first and/or the second reactor pyrolyzescomponents in the gas stream.
 5. The method according to claim 1 furthercomprising a water trap in the first and second modes of operation. 6.The method according to claim 1 wherein the stream of gas comprises theeluant flow from a gas chromatograph.
 7. The method according to claim 1wherein the isotope ratio is determined by using a mass spectrometer. 8.The method according to claim 1 wherein the mass spectrometer is anisotope ratio mass spectrometer.
 9. The method according to claimwherein the isotope ratio is determined by using an opticalspectrometer.